sample_muxer: Silence MSVC warning.
sample_muxer: Silence MSVC warning.

Disable C4996; A warning that encourages users to make their code
require the "secure" variant of functions like tmpnam(). Doing so
just happens to make the resulting code require the MSVC runtime.

Change-Id: I0329ce3aa93da060110d24a4bc7f48a7f9c87227

iniwf/webm.libwebm,kleopatra999/webm.libwebm,Acidburn0zzz/webm.libwebm,gshORTON/webm.libwebm,jdm/libwebm,felipebetancur/libwebm,reimaginemedia/webm.libwebm,Maria1099/webm.libwebm,matanbs/webm.libwebm,ericmckean/webm.libwebm,Suvarna1488/webm.libwebm,webmproject/libwebm,pcwalton/libwebm,kim42083/webm.libwebm,abwiz0086/webm.libwebm,zofuthan/libwebm,felipebetancur/libwebm,kalli123/webm.libwebm,webmproject/libwebm,zofuthan/libwebm,webmproject/libwebm